Scrub cleaning, which has the advantage of being capable of efficiently cleaning off particles such as polishing debris and abrasive particles contained in a polishing liquid, is widely employed these days in a cleaning apparatus of a semiconductor manufacturing apparatus, especially a chemical mechanical polishing (CMP) apparatus. In particular, scrub cleaning of a substrate with a roll cleaning tool is widely employed because of the advantages of not damaging the substrate, being capable of absorbing dirt such as a polishing liquid, having a high scraping effect, etc.
Cleaning of a substrate using a roll cleaning tool is performed by rubbing the roll cleaning tool against the substrate while rotating the substrate and supplying a cleaning liquid (e.g. a liquid chemical or pure water) to the substrate. By rubbing the roll cleaning tool against the surface of the substrate in the presence of the cleaning liquid, particles, such as polishing debris and abrasive particles contained in a polishing liquid, are removed from the surface of the substrate. The particles that have been removed from the substrate are absorbed or accumulated in the roll cleaning tool, or are discharged from the substrate together with the cleaning liquid.
However, some particles, once accumulated in the roll cleaning tool, can come off the roll cleaning tool and may be attached to the substrate surface again during scrub cleaning of the substrate, thus possibly causing so-called back contamination. Further, some particles, which have been once removed from the substrate surface by the roll cleaning tool, can be attached to the substrate surface again before the particles are discharged from the substrate along with the cleaning liquid.
For cleaning of a front surface of a substrate, a PVA (polyvinyl alcohol) sponge may be used in order to remove fine particles. When a substrate is held on a top ring which is a substrate holder, the substrate is brought into contact with a membrane and dirt may adhere to a back surface of the substrate due to a bonding force of the dirt acting on the substrate. In view of this, cleaning of the back surface of the substrate may be performed with use of a sponge of non-woven fabric comprising fibers bound by resin and having fine surface pores formed between fibers.
In the scrub cleaning with use of the cleaning member such as a roll sponge, the cleaning member is placed in direct contact with the substrate. Therefore, contamination of the cleaning member itself is a factor that influences the cleaning effect. As the contamination of the cleaning member progresses, a contaminant accumulated on the cleaning member can contaminate the substrate, while a contaminant is removed from the substrate. As a result, the cleaning effect cannot be obtained. Such a phenomenon is called back contamination. Such back contamination should be prevented as much as possible. Therefore, attempts are currently being made to prevent the back contamination.
A so-called self-cleaning method, which involves cleaning a cleaning member itself without replacing it even when it is contaminated, is used as a means for preventing the back contamination.
There are two main self-cleaning methods currently used.
The first method is a method called inner rinsing, which involves passing a cleaning liquid from an interior to an exterior of a roll sponge, thereby cleaning the roll sponge. This method, which cleans off dirt with the cleaning liquid in a simple manner, has the advantages of being capable of arbitrarily carrying out cleaning regardless of the structure of the roll cleaning machine used and the position of the roll, and not causing any unwanted damage to the sponge.
The second method is a method using a roll cleaning machine in which a roll sponge is configured to be retreated from a position on a substrate to a standby position, and involves providing a cleaning plate at the roll sponge standby position in order to clean the roll sponge during standby by rubbing the roll sponge against the cleaning plate.
Of the above-described two self-cleaning methods, the inner rinsing method, which involves passing the cleaning liquid from the interior to the exterior of a roll sponge so as to clean the roll sponge, has the drawback of low effect of cleaning off dirt clogging pores of the roll sponge, i.e. low cleaning effect.
The other method, which cleans the roll sponge in the standby position by rubbing the roll sponge against the cleaning plate, has the drawback that cleaning of the roll sponge can be carried out only when the roll sponge is in the standby position. Furthermore, the roll sponge is forced to keep pressing on the cleaning plate during the period when the roll sponge stays in the standby position, and the self-cleaning operation cannot be arbitrarily stopped during standby of the roll sponge. Thus, this method has the drawback of being incapable of arbitrarily controlling a self-cleaning time. This may cause early wear of the roll sponge if a set time of the standby is long.